--- name: AnimationConstraint last_updated: 2026-10-15T23:14:01Z inherits: - Constraint - Instance - Object type: class memory_category: BaseParts summary: "Aligns two BaseParts with an animate-able kinematic or force-based joint that supports physical simulation (ragdoll, arm strength). The default joint type for R15 avatar rigs." --- # Class: AnimationConstraint > Aligns two [BaseParts](/docs/reference/engine/classes/BasePart.md) with an animate-able kinematic or > force-based joint that supports physical simulation (ragdoll, arm strength). > The default joint type for R15 avatar rigs. ## Description #### Replaces Motor6D for Avatar rigs As part of the [Avatar Joint Upgrade](https://devforum.roblox.com/t/avatar-joint-upgrade-for-physically-simulated-character-movement-is-now-live/4298561), `AnimationConstraint` is the **replacement for [Motor6D](/docs/reference/engine/classes/Motor6D.md)** in [R15 player character rigs](/docs/en-us/avatar/character-bodies/specifications.md#rigging). When [AvatarJointUpgrade](/docs/reference/engine/classes/StarterPlayer.md) is enabled (the default for new experiences), player characters spawn with AnimationConstraints instead of Motor6Ds. Unlike Motor6D, AnimationConstraint supports both kinematic animation and force-based physical simulation — enabling ragdoll physics, arm strength, and other physically simulated character movement without rebuilding the rig. #### Migrating from Motor6D If you have existing code that uses Motor6D for character rigs, note these key differences. See also the [Phase 2 migration recommendations](https://devforum.roblox.com/t/avatar-joint-upgrade-aju-phase-2-rollout-updated-migration-recommendations/4656414). - **Finding joints**: Use `:FindFirstChildWhichIsA("AnimationConstraint")` instead of `:FindFirstChildOfClass("Motor6D")`. For code that must support both old and new rigs, check for AnimationConstraint first, then fall back to Motor6D. - **C0, C1, Part0, Part1**: These properties exist on AnimationConstraint as **read-only** aliases for backwards compatibility. They map to `Attachment0.CFrame`, `Attachment1.CFrame`, `Attachment0.Parent`, and `Attachment1.Parent` respectively. Do not attempt to write to them. - **Do not modify RigAttachment.CFrame directly** — this disrupts animation retargeting and causes performance issues. - **Transform**: Works identically to [Motor6D.Transform](/docs/reference/engine/classes/Motor6D.md) — the [Animator](/docs/reference/engine/classes/Animator.md) writes to it each frame. Layer procedural animations by multiplying into `Transform` during [RunService.PreSimulation](/docs/reference/engine/classes/RunService.md), which stacks with active animation tracks without breaking retargeting. - **IsKinematic**: When `true` (default), behavior is equivalent to Motor6D. Set to `false` to enable force-based physical simulation. - **Type checks**: `animConstraint:IsA("Motor6D")` returns `false`. Update any `IsA("Motor6D")` guards to also accept `"AnimationConstraint"`. - **Server replication**: Instead of setting C0 on the server, use client-side animation evaluation and synchronize data through custom Attributes or [UnreliableRemoteEvent](/docs/reference/engine/classes/UnreliableRemoteEvent.md). ##### Example: Procedural neck rotation ```lua -- Before (Motor6D): writing to C0 directly local originalC0 = neck.C0 RunService.RenderStepped:Connect(function() neck.C0 = originalC0 * computeNeckRotation() end) -- After (AnimationConstraint): multiplying into Transform during PreSimulation RunService.PreSimulation:Connect(function() if not animator.EvaluationThrottled then neck.Transform = computeNeckRotation() * neck.Transform end end) ``` #### Description An `AnimationConstraint` constrains its [Attachments](/docs/reference/engine/classes/Attachment.md) so that they're offset by [Transform](/docs/reference/engine/classes/AnimationConstraint.md). When [IsKinematic](/docs/reference/engine/classes/AnimationConstraint.md) is `true`, the parts follow the transform perfectly (identical to Motor6D behavior). When `false`, the constraint applies forces and torques limited by [MaxForce](/docs/reference/engine/classes/AnimationConstraint.md) and [MaxTorque](/docs/reference/engine/classes/AnimationConstraint.md), enabling physically simulated character movement. ## Properties ### Property: AnimationConstraint.AngularDamping ```json { "type": "float", "access": "ReadWrite", "security": { "read": "None", "write": "None" }, "serialization": { "can_load": true, "can_save": true }, "thread_safety": "ReadSafe", "category": "Compliance", "capabilities": [ "Physics", "Animation" ], "simulationAccess": true } ``` The damping ratio (ζ) applied to the rotational part of the constraint. Only used if [IsKinematic](/docs/reference/engine/classes/AnimationConstraint.md) is `false`. A value of `1` corresponds to **critical damping**, where the constraint reaches its target orientation as fast as possible without overshoot in the absence of other forces or constraints. Values less than `1` are under-damped and oscillate around the target before settling. Values greater than `1` are over-damped and approach the target more slowly without oscillation. A value of `0` applies no angular damping, causing the constraint to oscillate. Even with this property set to `1`, an `AnimationConstraint` at the root of a multi-body mechanism may still exhibit low-frequency oscillation because it does not "see" the full effective mass of the downstream chain. You can compensate by increasing both [AngularStrength](/docs/reference/engine/classes/AnimationConstraint.md) and `AngularDamping` beyond their defaults. ### Property: AnimationConstraint.AngularStrength ```json { "type": "float", "access": "ReadWrite", "security": { "read": "None", "write": "None" }, "serialization": { "can_load": true, "can_save": true }, "thread_safety": "ReadSafe", "category": "Compliance", "capabilities": [ "Physics", "Animation" ], "simulationAccess": true } ``` Controls how rigidly the constraint enforces the rotational part of its target [Transform](/docs/reference/engine/classes/AnimationConstraint.md). Only used if [IsKinematic](/docs/reference/engine/classes/AnimationConstraint.md) is `false`. The resulting torque is capped by [MaxTorque](/docs/reference/engine/classes/AnimationConstraint.md). `AngularStrength` is defined as a normalized natural frequency, `AngularStrength = f / 60`, where `f` is the target natural frequency in Hz. The default value of `1` corresponds to a target frequency of 60 Hz and produces strong tracking of the target orientation. A value of `0` applies no torque. Values less than `1` produce a softer, more compliant rotational response, and values greater than `1` produce a stiffer response. Use values significantly greater than `1` with caution, as they may cause the simulation to become unstable. ### Property: AnimationConstraint.IsKinematic ```json { "type": "boolean", "access": "ReadWrite", "security": { "read": "None", "write": "None" }, "serialization": { "can_load": true, "can_save": true }, "thread_safety": "ReadSafe", "category": "Data", "capabilities": [ "Physics", "Animation" ], "simulationAccess": true } ``` When `true`, the connected parts follow the [Transform](/docs/reference/engine/classes/AnimationConstraint.md) perfectly without participating in physics simulation. When `false`, the connected parts follow the trajectory using forces and torques limited by [MaxForce](/docs/reference/engine/classes/AnimationConstraint.md) and [MaxTorque](/docs/reference/engine/classes/AnimationConstraint.md). ### Property: AnimationConstraint.LinearDamping ```json { "type": "float", "access": "ReadWrite", "security": { "read": "None", "write": "None" }, "serialization": { "can_load": true, "can_save": true }, "thread_safety": "ReadSafe", "category": "Compliance", "capabilities": [ "Physics", "Animation" ], "simulationAccess": true } ``` The damping ratio (ζ) applied to the translational part of the constraint. Only used if [IsKinematic](/docs/reference/engine/classes/AnimationConstraint.md) is `false`. A value of `1` corresponds to **critical damping**, where the constraint reaches its target position as fast as possible without overshoot in the absence of other forces or constraints. Values less than `1` are under-damped and oscillate around the target before settling. Values greater than `1` are over-damped and approach the target more slowly without oscillation. A value of `0` applies no linear damping, causing the constraint to oscillate. `LinearDamping` has no effect when [LinearStrength](/docs/reference/engine/classes/AnimationConstraint.md) is `0`. ### Property: AnimationConstraint.LinearStrength ```json { "type": "float", "access": "ReadWrite", "security": { "read": "None", "write": "None" }, "serialization": { "can_load": true, "can_save": true }, "thread_safety": "ReadSafe", "category": "Compliance", "capabilities": [ "Physics", "Animation" ], "simulationAccess": true } ``` Controls how rigidly the constraint enforces the translational part of its target [Transform](/docs/reference/engine/classes/AnimationConstraint.md). Only used if [IsKinematic](/docs/reference/engine/classes/AnimationConstraint.md) is `false`. The resulting force is capped by [MaxForce](/docs/reference/engine/classes/AnimationConstraint.md). `LinearStrength` uses the same normalized natural frequency definition as [AngularStrength](/docs/reference/engine/classes/AnimationConstraint.md), `LinearStrength = f / 60`, where `f` is the target natural frequency in Hz. The default value of `1` corresponds to a target frequency of 60 Hz and produces strong tracking of the target position. A value of `0` applies no force. Values less than `1` produce a softer, more compliant positional response, and values greater than `1` produce a stiffer response. Splitting angular and linear parameters lets you make orientation tracking stiff while keeping positional tracking soft, or vice-versa. As with [AngularStrength](/docs/reference/engine/classes/AnimationConstraint.md), use values significantly greater than `1` with caution, as they may cause the simulation to become unstable. ### Property: AnimationConstraint.MaxForce ```json { "type": "float", "access": "ReadWrite", "security": { "read": "None", "write": "None" }, "serialization": { "can_load": true, "can_save": true }, "thread_safety": "ReadSafe", "category": "Compliance", "capabilities": [ "Physics", "Animation" ], "simulationAccess": true } ``` Maximum force magnitude the constraint can apply to achieve its goal. Only used if [IsKinematic](/docs/reference/engine/classes/AnimationConstraint.md) is `false`. ### Property: AnimationConstraint.MaxTorque ```json { "type": "float", "access": "ReadWrite", "security": { "read": "None", "write": "None" }, "serialization": { "can_load": true, "can_save": true }, "thread_safety": "ReadSafe", "category": "Compliance", "capabilities": [ "Physics", "Animation" ], "simulationAccess": true } ``` Maximum torque the constraint can use to reach its goal. Only used if [IsKinematic](/docs/reference/engine/classes/AnimationConstraint.md) is `false`. ### Property: AnimationConstraint.Transform ```json { "type": "CFrame", "access": "ReadWrite", "security": { "read": "None", "write": "None" }, "serialization": { "can_load": true, "can_save": true }, "thread_safety": "ReadSafe", "category": "Data", "capabilities": [ "Physics", "Animation" ], "simulationAccess": true } ``` The internal [CFrame](/docs/reference/engine/datatypes/CFrame.md) that is manipulated when the constraint is being animated. Note that `AnimationConstraint` transforms are not applied immediately, but rather as a batch in a parallel job after [RunService.PreSimulation](/docs/reference/engine/classes/RunService.md), immediately before physics steps. The deferred batch update is much more efficient than many immediate updates. If the `AnimationConstraint` is part of an animated model with an [Animator](/docs/reference/engine/classes/Animator.md), then [Transform](/docs/reference/engine/classes/AnimationConstraint.md) is usually overwritten every frame by the [Animator](/docs/reference/engine/classes/Animator.md) after [RunService.PreAnimation](/docs/reference/engine/classes/RunService.md) and before [RunService.PreSimulation](/docs/reference/engine/classes/RunService.md). ## Inherited Members ### From [Constraint](/docs/reference/engine/classes/Constraint.md) - **Property `Active`** (`boolean`): Indicates if the constraint is currently active in the world. - **Property `Attachment0`** (`Attachment`): The Attachment that is connected to - **Property `Attachment1`** (`Attachment`): The Attachment that is connected to - **Property `Color`** (`BrickColor`): The color of the constraint. - **Property `Enabled`** (`boolean`): Toggles whether or not the constraint is enabled. - **Property `Visible`** (`boolean`): Toggles the constraint's visibility. - **Method `GetDebugAppliedForce(bodyId: int): Vector3`**: *(deprecated)* - **Method `GetDebugAppliedTorque(bodyId: int): Vector3`**: *(deprecated)* ### From [Instance](/docs/reference/engine/classes/Instance.md) - **Property `Archivable`** (`boolean`): Determines if an Instance and its descendants can be cloned using - **Property `archivable`** (`boolean`): *(deprecated, hidden)* - **Property `Capabilities`** (`SecurityCapabilities`): The set of capabilities allowed to be used for scripts inside this - **Property `IsInSandbox`** (`boolean`): Indicates whether the instance is inside a sandboxed container. - **Property `Name`** (`string`): A non-unique identifier of the Instance. - **Property `Parent`** (`Instance`): Determines the hierarchical parent of the Instance. - **Property `PredictionMode`** (`PredictionMode`): Reflects the client-side prediction mode applied to the instance under - **Property `RobloxLocked`** (`boolean`): A deprecated property that used to protect CoreGui objects. *(hidden)* - **Property `Sandboxed`** (`boolean`): When enabled, the instance can only access abilities in its `Capabilities` - **Property `UniqueId`** (`UniqueId`): A unique identifier for the instance. - **Method `AddTag(tag: string): ()`**: Applies a tag to the instance. - **Method `children(): Instances`**: Returns an array of the object's children. *(deprecated)* - **Method `ClearAllChildren(): ()`**: This method destroys all of an instance's children. - **Method `Clone(): Instance`**: Create a copy of an instance and all its descendants, ignoring instances - **Method `clone(): Instance`**: *(deprecated)* - **Method `Destroy(): ()`**: Sets the Instance.Parent property to `nil`, locks the - **Method `destroy(): ()`**: *(deprecated)* - **Method `FindFirstAncestor(name: string): Instance?`**: Returns the first ancestor of the Instance whose - **Method `FindFirstAncestorOfClass(className: string): Instance?`**: Returns the first ancestor of the Instance whose - **Method `FindFirstAncestorWhichIsA(className: string): Instance?`**: Returns the first ancestor of the Instance for whom - **Method `FindFirstChild(name: string, recursive?: boolean): Instance?`**: Returns the first child of the Instance found with the given name. - **Method `findFirstChild(name: string, recursive?: boolean): Instance`**: *(deprecated)* - **Method `FindFirstChildOfClass(className: string): Instance?`**: Returns the first child of the Instance whose - **Method `FindFirstChildWhichIsA(className: string, recursive?: boolean): Instance?`**: Returns the first child of the Instance for whom - **Method `FindFirstDescendant(name: string): Instance?`**: Returns the first descendant found with the given Instance.Name. - **Method `GetActor(): Actor?`**: Returns the Actor associated with the Instance, if any. - **Method `GetAttribute(attribute: string): Variant`**: Returns the value which has been assigned to the given attribute name. - **Method `GetAttributeChangedSignal(attribute: string): RBXScriptSignal`**: Returns an event that fires when the given attribute changes. - **Method `GetAttributes(): Dictionary`**: Returns a dictionary of the instance's attributes. - **Method `GetChildren(): Instances`**: Returns an array containing all of the instance's children. - **Method `getChildren(): Instances`**: *(deprecated)* - **Method `GetDebugId(scopeLength?: int): string`**: Returns a coded string of the debug ID used internally by Roblox. - **Method `GetDescendants(): Instances`**: Returns an array containing all of the descendants of the instance. - **Method `GetFullName(): string`**: Returns a string describing the instance's ancestry. - **Method `GetStyled(name: string, selector: string?): Variant`**: Returns the styled or explicitly modified value of the specified property, - **Method `GetStyledPropertyChangedSignal(property: string): RBXScriptSignal`**: Returns an event that fires when the given style property changes on the - **Method `GetTags(): Array`**: Gets an array of all tags applied to the instance. - **Method `HasTag(tag: string): boolean`**: Check whether the instance has a given tag. - **Method `IsAncestorOf(descendant: Instance): boolean`**: Returns true if an Instance is an ancestor of the given - **Method `IsDescendantOf(ancestor: Instance): boolean`**: Returns `true` if an Instance is a descendant of the given - **Method `isDescendantOf(ancestor: Instance): boolean`**: *(deprecated)* - **Method `IsPropertyModified(property: string): boolean`**: Returns `true` if the value stored in the specified property is not equal - **Method `QueryDescendants(selector: string): Instances`**: Returns an array containing all descendants of the instance that match the - **Method `Remove(): ()`**: Sets the object's `Parent` to `nil`, and does the same for all its *(deprecated)* - **Method `remove(): ()`**: *(deprecated)* - **Method `RemoveTag(tag: string): ()`**: Removes a tag from the instance. - **Method `ResetPropertyToDefault(property: string): ()`**: Resets a property to its default value. - **Method `SetAttribute(attribute: string, value: Variant): ()`**: Sets the attribute with the given name to the given value. - **Method `WaitForChild(childName: string, timeOut: double): Instance`**: Returns the child of the Instance with the given name. If the - **Event `AncestryChanged`**: Fires when the Instance.Parent property of this object or one of - **Event `AttributeChanged`**: Fires whenever an attribute is changed on the Instance. - **Event `ChildAdded`**: Fires after an object is parented to this Instance. - **Event `childAdded`**: *(deprecated)* - **Event `ChildRemoved`**: Fires after a child is removed from this Instance. - **Event `DescendantAdded`**: Fires after a descendant is added to the Instance. - **Event `DescendantRemoving`**: Fires immediately before a descendant of the Instance is removed. - **Event `Destroying`**: Fires immediately before (or is deferred until after) the instance is - **Event `StyledPropertiesChanged`**: Fires whenever any style property is changed on the instance, including ### From [Object](/docs/reference/engine/classes/Object.md) - **Property `ClassName`** (`string`): A read-only string representing the class this Object belongs to. - **Property `className`** (`string`): *(deprecated)* - **Method `GetPropertyChangedSignal(property: string): RBXScriptSignal`**: Get an event that fires when a given property of the object changes. - **Method `IsA(className: string): boolean`**: Returns true if an object's class matches or inherits from a given class. - **Method `isA(className: string): boolean`**: *(deprecated)* - **Event `Changed`**: Fires immediately after a property of the object changes, with some